1. Field Of The Invention:
This invention relates to a cross-linked, melt-flowable thermoplastic elastomer blend and a method of making same.
2. Description Of The Prior Art:
Blends of monoolefin polymer rubbers, e.g., ethylenepropylene copolymer elastomers and ethylene, propylene and copolymerizable polyene terpolymer elastomers, with polyolefins, e.g., high density polyethylene, polypropylene and the like, which can be processed and fabricated by methods used for thermoplastics and have elastomeric properties without requiring vulcanization are well-known. Furthermore, thermoplastic elastomer blends of partially cured monoolefin copolymer rubbers and certain polyolefins are known. See, for example, U.S. Pat. Nos. 3,758,642 and 3,806,588. It is disclosed in both of these prior art patents that the partial curing of the monoolefin copolymer rubber is essential to produce a blend which has the characteristics of a thermoplastic resin, i.e., which can be reprocessed, while also having elastomeric characteristics.
However, known thermoplastic elastomer blends of monoolefin polymer rubbers and polyolefin resins suffer from the disadvantage of having less than desirable overall balance of mechanical or physical properties, such as low resiliency, tensile strength, stiffness, surface hardness, and/or high heat distortion, permanent or tension set, etc. Furthermore, many known blends, including blends prepared in accordance with the teachings of the above-mentioned U.S. Pat. Nos. 3,758,643 and 3,806,558 or U.S. Pat. No. 3,835,201, have less than desirable melt rheologies, e.g., high viscosity at high shear rates at the high melt temperatures normally used in injection molding. Such undesirable characteristics restrict the use of such known thermoplastic elastomer blends in the manufacture of many types of flexible molded or extruded articles. This is particularly evident in the manufacture of flexible body components for the automotive industry. For such a use, a thermoplastic elastomer is required which has such characteristics as relatively low viscosity at high shear rates at melt temperatures for use in high-speed injection molding or extrusion techniques to provide flexible body components having high resiliency, tensile strength, flexural modulus, etc. along with low permanent set, heat distortion and the like.